Add bcm2708_gpio driver

Signed-off-by: popcornmix <popcornmix@gmail.com>

bcm2708: Add extension to configure internal pulls

The bcm2708 gpio controller supports internal pulls to be used as pull-up,
pull-down or being entirely disabled. As it can be useful for a driver to
change the pull configuration from it's default pull-down state, add an
extension which allows configuring the pull per gpio.

Signed-off-by: Julian Scheel <julian@jusst.de>

bcm2708-gpio: Revert the use of pinctrl_request_gpio

In non-DT systems, pinctrl_request_gpio always fails causing
"requests probe deferral" messages. In DT systems, it isn't useful
because the reference counting is independent of the normal pinctrl
pin reservations.

gpio: Only clear the currently occurring interrupt. Avoids losing interrupts

See: linux #760

bcm2708_gpio: Avoid calling irq_unmask for all interrupts

When setting up the interrupts, specify that the handle_simple_irq
handler should be used. This leaves interrupt acknowledgement to
the caller, and prevents irq_unmask from being called for all
interrupts.

Issue: linux #760